The bacterial second message c-di-GMP signaling pathways mainly involve signal metabolism,signal recognition by receptor,reception and transduction,and phenotype expression and regulation.The intracellular level of c-di-GMP is precisely controlled by diguanylate cyclases(DGC)and phosphodiesterase(PDE)via biosynthesis or degradation,respectively.Several c-di-GMP receptors have been identified and characterized from various bacterial species,including transcription regulator,PilZ-domain protein,degenerate GGD...